DEM simulation of small strain and large strain behaviors of granular soils with a coherent contact model

Discrete element method is widely used to study the macroscopic behaviors of granular soils subjected to various loading conditions at a particulate level. However, most of previous studies used different contact models to simulate soil behaviors at different strain levels. To reconcile the disparities between different contact models in DEM simulation, a modified rolling resistance Hertz-Mindlin model is proposed for simultaneously emulating distinct behaviors of granular soils at both small strain and large strain. The Hertz-Mindlin contact model is used to capture the stress-dependent small strain stiffness, while the rolling resistance model is adopted to capture the main effect of particle shape. Contact stiffness degradation is also taken into consideration in the simulation. The comparisons with experimental data show that the model used in this paper can effectively capture the essential features of soil behaviors at both small and large strains in drained and undrained triaxial shear tests. The results indicate that contact stiffness degradation during shearing should be considered for avoiding irrationally high negative excess pore water pressure in undrained triaxial shearing. Incorporation of rolling resistance into the contact model is necessary for reaching a reasonably high critical state stress ratio arising from particle shape.